Pressure roller plate with force distribution

ABSTRACT

Printer ( 1 ) feeds paper or other media sheets ( 5 ) to pinch rollers ( 9   a,    9   b ), which further feed the sheets into an imaging station ( 7 ). Pressure rollers ( 9   b ) are held by plate  22  which is biased by a spring ( 33 ) and pivots on extensions ( 37   a   , 37 ) to moves pressure rollers ( 9   b ) into nip relationship with nip roller ( 9   a ). To evenly distribute the forces across pressure rollers ( 9   b ), plate  22  is weakened by depressed lines ( 27   a,    27   b ) located between the spring and the pressure rollers ( 9   b ).

TECHNICAL FIELD

This invention relates to apparatus to apply pressure evenly to rollers forming a nip with a drive roller for sheet feed, such as in printers and other imaging devices,

BACKGROUND OF THE INVENTION

Advancing of paper and other sheets through two rollers forming a nip is highly conventional in printers and other imaging devices. Typically one of the rollers is driven from a motor and the second roller turns freely while it applies pressure to keep the rollers nipped against the sheets. Typically, the pressure rollers are supported by cantilevered plate or the like which is rotated toward the nip by a spring. It is known to bevel or weaken the ends of rollers to reduce damaging forces.

It has been discovered in accordance with this invention that the pressure roller plate may induce significant pressure differences on the pressure roller along it length. The tends to skew sheets being fed. When the second or driven roller is compliant enough to absorb differences in a pressure roller pressures, along its length, such pressure differences have been tolerable. However, reliable, forward sheet feeding can be improved by eliminating such differences. This permits the drive roller to be less compliant, which contributes to the reliable sheet feeding.

The pressure roller plate of the disclosed embodiment of this invention in general form and in primary function is essentially the same as pressure plates previously employed in printers constituting prior art to this invention. This invention differs in the plate having different bending characteristics between the pressure application point and the part of the plate at which rollers are supported.

DISCLOSURE OF THE INVENTION

This invention includes a pressure plate for supporting one or more pressure rollers. The pressure plate connects to a spring at one location and has pivot locations which contact frame members at opposite locations spaced from the spring-connection location. The plate is weakened at location intermediate the spring-connection location and locations supporting the pressure roller or rollers.

In an embodiment, the plate is generally rectangular, with a spring-connection location generally central on one side (the spring connection side). Two pivot surfaces are somewhat forward of the spring-connection and are spaced from the spring connection to locations generally near the two sides of the plate leading away from the spring connection side (the lateral sides of the plate). Two rollers are held on the side of the plate opposite the spring-connection location, each roller being positioned generally from the center of the plate to the lateral side of the plate. The two rollers are held in resilient, C-shaped elements partially surrounding their shafts to be parallel to the roller holding side. The plate is of a single material which has a thinned portion beginning generally near the center and connecting to the sides leading from the spring connection. In an embodiment this weakened part is a depression located from generally near the center of one side to generally near the far ends of the other sides in a somewhat V shape when viewed from the top.

DESCRIPTION OF THE DRAWINGS

The details of this invention will be described in connection with the accompanying drawings, in which

FIG. 1 is illustrative of a printer or other imaging device employing this invention,

FIG. 2 is a perspective view from the right rear showing one pressure plate as mounted with associated frame parts and the nip rollers,

FIG. 3 is a perspective view from the left rear showing one pressure plate a mounted with associated frame parts and the spring for providing nip force,

FIG. 4 is a cross-section from the left side showing a pivot member and a part of the depressed area,

FIG. 5 is a top view of an embodiment of the pressure plate,

FIG. 6 shows actually measured force distributions along the roller without the invention, and

FIG. 7 shows measured actual force distributions along the roller with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is illustrative of a printer 1 in which this invention would be employed. Printer 1 may be a standard inkjet printer in most respects. As such it has a bottle printhead 3 which jets dots of ink through nozzles not shown, which are located above a sheet 5 of paper or other media at a imaging station 7

Imaging station 7 is located past nip rollers 9 a, 9 b (see FIG. 2) which grasp paper 5 in the nip of rollers 9 a, 9 b and move it under printhead 3. Nip rollers 9 a, 9 b are stopped normally several times to permit printhead 3 to partially image sheet 5 by moving across sheet 5 (in and out of the view of FIG. 1) while expelling dots in the desired pattern. In a draft mode the number of such intermittent stops may be only two, while in a quality mode that number may be five or more.

With reference to FIG. 2 pressure roller 9 b is held against drive roller 9 a by pressure plate 22. With reference to FIG. 1 nip roller 9 a, 9 b push paper through the imaging station 7 where they enter exits rollers 11 a, 11 b, 11 c, and 11 d. This invention is to biasing the nip rollers 9 a, 9 b employing pressure plate 22.

The printer of FIG. 1 has a paper tray 13 located on the bottom Tray 13 constitutes a bin in which a stack of paper or other media sheets 5 are held to be imaged. Having tray 13 located on the bottom of printer 1 permits a large stack of sheets 5 to be in the printer 1. This spaces the tray 13 from the print stations 7, the distance from pick roller 15 a of tray 13 to nip rollers 9 a, 9 b being longer than the length of some media sheets 5 to be printed. Pick roller 15 a is a part of an autocompensating swing mounted system 15.

A C-shaped paper guide 17 is made up of rear guide surface 17 a and spaced, generally parallel, front guide surface 17 b. Both surfaces have spaced ridges (not shown), as is common. Guide 17 directs a sheet 5 to nip rollers 9 a, 9 b. Intermediate in guide 17 is drive roller 19 a, which is a part of an autocompensating swing-mounted system 19. Sensor arm 21 is moved by a sheet 5 to detect the sheet 5 at system 19.

Pick roller 15 a at tray 13 and drive roller 19 a combine to move sheets 5 from tray 13 to nip rollers 9 a, 9 b. Drive roller 19 a is effective to move short media into rollers 9 a, 9 b, when pick roller 15 a is no longer in contact with the sheet 5.

Operational control is by electronic data processing apparatus, shown as element C in FIG. 1. Such control is now entirely standard. A standard microprocessor may be employed, although an Application Specific Integrated Circuit (commonly known as an ASIC) is also employed, which is essentially a special purpose computer, the purpose being to control all actions and timing of printer 1. Electronic control is so efficient and versatile that mechanical control by cams and relays and the like is virtually unknown in imaging. However, such control is not inconsistent with this invention.

FIG. 2 shows the pressure plate 22 supporting pressure rollers 9 b against a drive roller 9 a. In a full implementation of the embodiment shown, three such pressure plates 22 would be located and held across the frame shown, thereby supporting six rollers 9 b. The pressure plates would be located on each side of opening 25 through which a paper-presence sensor arm (not shown) protrudes in the completed assembly.

Frame 23 where it supports plate 22 is of thin, rigid sheet metal. It has tabs 23 a folded to form ledges on which plate 22 pivots as will be described. Plate 9 a is a molded, generally rectangular single piece of rigid polycarbonate which is generally of at least one thickness, except at depressed lines 27 a and 27 b. Depressed lines 27 a and 27 b are to weaken plate 22 for bending.

FIG. 2 shows a small part of a locating ridge 29 extending through a mating slot in frame 23. FIG. 3 shows ridge 29 from the opposite side. Ridge 29 in frame 23 holds plate 22 from moving laterally with respect frame 23. Upward extensions 31 a and 31 b, on opposite lateral sides of plate 22, position plate 22 against frame 23.

Spring 33 is connected between frame 23 and a spring connecting bar 35 which is generally central on the side of plate 22 spaced from the side holding rollers 21. Also shown in FIG. 3, but one being best shown in FIG. 4, are rounded, pivot extensions 37 a, 37 b. These contact tabs 23 a of frame 23. Pivot extensions 37 a, 37 b are located on opposite sides of spring connecting bar 35 near the lateral ends of the spring connecting side of plate 22.

FIG. 4, being a cross-section, shows one location of depression line 27 a. FIG. 4 shows C-shaped, resilient holding part 41 a which holds a shaft of roller 9 a by flexing to receive the shaft as is entirely standard. Corresponding part shown are labeled as 41 b and 41 c in FIG. 5.

FIG. 5 is a top view of plate 22 alone and therefore shows lines 27 a and 27 b extending from the roller holding side of plate 22 to the lateral sides of plate 22. Ribs 39 a, 39 aa, 39 aaa, 39 b, 39 bb, 39 bbb, as well as central, generally semicircular raised part 41 are for stiffening. Such subject matter is not generally novel with respect to this invention. Depressed channels 27 a, 27 b are for weakening and are novel with this invention.

This invention recognizes that spring 33 operates to bow the center of plate 22 upward, thereby providing the highest forces of the lateral sides of plate 22. By weakening plate 22 between the center of plate 22 and the roller holding part, the plate tends to flatten, which more evenly distributes the forces on rollers 9 b.

FIG. 6 and FIG. 7 show actual measurements of two comparable systems, one, FIG. 7, employing this invention and one, FIG. 6, not employing this invention. The horizontal axis of each is in nominal, linear units which extend across the entire length of a roller comparable to roller 9 b. The vertical axis of each is in nominal, linear units of measured force. The improved distribution of forces shown in FIG. 7 is very evident.

Clearly, the pressure plate can take many forms which are pivoted by spring action or the like and which are subject to being bowed by that spring action. The weakening can be in any manner including employing more still material near the spring connection and less stiff material between the more stiff material and the pressure rollers. 

1. An imaging device comprising a sheet feed path, a drive roller in said sheet feed path, a pressure roller, a plate holding said pressure roller by spring force for rotation in nip relationship with said drive roller, said plate comprising a spring connection location to receive a spring to provide said spring force, a pressure roller holding location on a side opposite side spring connection location, said pressure roller being held at said pressure roller hold location in nip with said drive roller, and a weakened portion between said print connection location and said pressure roller holding location.
 2. The imaging device as in claim 1 in which said plate holds two pressure rollers and said spring connection location is located generally intermediate said two pressure rollers.
 3. The imaging device as in claim 1 in which said weakened portion is a depressed portion in said plate.
 4. The imaging device as in claim 3 in which said depressed portion in said plate is a line extending generally between the center of said pressure roller holding location to one lateral side of said plate and a line extending generally between the center of said pressure roller holding location and the other lateral side of said plate, thereby forming a somewhat V shape when viewed from the top of said plate.
 5. An imaging device comprising a sheet feed path, a drive roller in said sheet feed path, two pressure rollers, a plate holding said pressure rollers by spring force for rotation in nip relationship with said drive roller, said plate comprising a spring connection side having a generally central spring connection location, a pressure roller holding side opposite said spring connection side holding said two rollers generally from the center of said plate to the lateral sides of said plate, and a weakened portion between said print connection side and said pressure roller holding side.
 6. The imaging device as in claim 5 in which said weakened portion is a depressed portion in said plate.
 7. The imaging device as in claim 6 in which said depressed portion in said plate is a line extending generally between the center of said pressure roller holding location to one lateral side of said plate and a line extending generally between the center of said pressure roller holding location and the other lateral side of said plate, thereby forming a somewhat V shape when viewed from the top of said plate. 